Hi, I have been reading some about symmetry and I have a couple of questions that I hope you can answer.

1: when a layup is written +45/-45 why do you go about having minus and plus. Is that only applicable when using unidirectional fibers ? Or is it applicable when using a twill 2x2 as well (If yes, then why)? 

2. I have read that if you are doing a flat panel then symmetry can be important to mitigate warping. How are you thinking about symmetry of your layup ? For exempel when doing complex shapes ? I are you always striving for it in any layup ?

3. When doing flat parts with core I have read that it might be good to have more layers on the side of the core that will bend. If doing that won’t you disrupt the symmetry when the is core is counted as midplane ?

4. Does a two layer layup of 0/45 count as symetrical when there is no mid plane?

Thank you, 

Thank you Warren for your answer! I got some new questions.

What will the effect be if you have a twill and rotate it -45 ?

when thinking about a layup and warping do you know the effect of having different cloth weight. For example if you are doing a layup with 210g 0deg with a 400g in 45deg. Will the 400g count as two 210g in the 45deg orientation?

do you have any sources e.g books or webpages to read up on this ?

thank you